Rat Plague on Ships at AmsterdamMr. A. Vedder publishes in the Nederlandsch tijdschrift voor geneeskunde a study on plague. Between 1910 and 1930, plague-infected rats were found eight times on ships in the port of Amsterdam, the last discovery being in 1920. In 1932, renewed manifestations of rat plague developed on a ship coming from the Plata River. The author, who examined the rats sent to the university laboratory, emphasized the resemblance of the plague bacillus to the bacillus of pseudotuberculosis rodentium. The two have the same morphologic characteristics, the same typical forms of colonies, and the same biochemical reactions, and in inoculations into the guinea-pig only the Otten test made differentiation possible.Like Bacillus pseudotuberculosis-rodentium, the plague bacillus presents three different types of colonies. In the former there is an evident relation between the degree of virulence and the form of the colonies. The same is probably true